The invention""s primary application is with theater projection and the like, specifically with 35 mm film.
The invention relates to a luminous projection lens.
A luminous projection lens equipped with 7 lenses is described in applicants"" published European patent application 00 100 890.3. This 7 lens system is not particularly suited for systems which require shorter focal lengths and/or larger image fields. Additional problems associated with such 7 lens systems include keeping a certain minimum back focal length and minimum overall length depending on the image angle, which may not be exceeded due to installation provisions or application constraints.
Those types of lens systems which meet the above noted requirements more appropriately, are similar to those of typical wide angle lenses with inverse configurations. Such lens systems have been known for a long time and were described in many patent documents. However, such prior lens systems, have a diaphragm position adapted to certain predetermined correction requirements, and must therefore submit to or be used with these requirements. The provisions of bundle geometry according to the present invention are not met by any of these prior lens systems.
More specifically, these types of prior lens systems can be categorized and summarized as follows:
Each of the 7-lens systems disclosed in U.S. Pat. Nos. 4,537,476; 4,468,100; 4,176,914; 3,874,770, and DE-OS 2551583, DE-AS 1472135 contain the basic system configuration necessary to obtain good projection quality with a large aperture and large fields in a retrofocus style. However, the projection quality that can be achieved is insufficient for the target values needed in these cases (a contrast of 60 LP/mm greater than 40% throughout an entire image field, distortion xe2x89xa61%). The same also applies to the 8-lens and 9-lens systems of patents DE-AS 2443319, DE-OS 2321864; U.S. Pat. Nos. 4,566,764, 3,736,049, which also contain doublets that are precluded with the application purpose at hand.
Patents DE-OS 2554963, DE-OS 2306346, DE-PS 2512797, DE-PS 2514081, DE-PS 2436444, DE-OS 2359156, DE-PS 2344224, DE-OS 2254586 describe modified lens systems of the aforementioned basic types with lenses numbered from 7 to 12 lenses, and preference is also given to an aspheric surface design.
This is similar with systems in patent documents U.S. Pat. Nos. 5,724,195, 5,684,643, 5,625,497 and 5,477,389, in which aspheric surfaces, lenses numbered from 7 to 9 and extremely short focal lengths are preferred. The patent claims formulated in this document are essentially kept much more general, as the claims first of all differentiate only between an anterior and posterior assembly with a diaphragm positioned in between, and consequently a certain number of requirements are devised. These requirements, however, apply only in their entirety, as individual requirements are partially the basis for claims in the aforementioned and other patent documents (such as e.g. DE-PS 2514081, same as U.S. Pat. No. 4,025,169). Some of these requirements are also met entirely or partly by a system configuration according to the invention. Albeit, the requirements of bundle geometry according to the present invention are completely unaffected by this.
In summary, the following can be stated: The lens systems disclosed in the aforementioned documents meet neither the requirements of bundle geometry according to the present invention, nor the quality requirements for the projection performance necessary throughout an entire image field giving consideration to the number of lenses.
Furthermore, these prior lens systems were partly designed giving preference to aspheric surfaces as well as doublets. Neither are required in the lens system configuration of the present invention.
The purpose of the invention is to provide lens, and in particular a series of lenses, which on one hand meet the most effective use of light distribution across an entire object field, and on the other hand have a projection quality greater or the same as the projection quality of known technical solutions when using technologically favorable glasses.
One aspect of the invention relates to a projection lens that is composed of nine lenses with bilateral air-glass surfaces. The aim of the invention is to provide a lens or a series of lenses that guarantee the most effective light distribution across the entire object field while offering a projection quality that is greater than or equal to the projection quality of the known technical solutions while creating technologically favorable glasses. To this end, the projection lens according to the invention meets the following requirements in their entirety: uxe2x89xa712.8xc2x0, 100 mm xe2x89xa6LEPxe2x89xa6400 mm, xcex1 RBaxe2x89xa71xc2x0, xcex1 RBixe2x89xa6xe2x88x9214xc2x0, with u being the orifice angle (2 u total angle) at the illumination side, LEP being the distance of the entrance pupil (illumination side) from the object plane (position in the direction of projection from the reference point of the object plane is a positive value), xcex1 RBa being the angular tilt of the beam with respect to the optical axis in the object space between the object and the first lens surface of the lens that delimits the bundle for the field edge (outer field point in the object) towards the exterior (away from the optical axis, axis-remote), and xcex1 RBi being the angular tilt of the beam with respect to the optical axis in the object space between the object and the first lens surface of the lens that delimits the bundle for the field edge (outer field point in the object) towards the interior (towards the optical axis, axis-close). The angles xcex1 RBa and xcex1 Rbi are positive if the corresponding beams intersect the optical axis in a point that lies in the opposite direction of projection when seen from the object, and they are negative if they intersect the optical axis in a point that lies in the direction of projection when seen from the object. The lenses are positioned in the following sequence, starting from the image (blow-up side) towards the object (reduction and illumination side): a fist negative, meniscus-shaped lens (1), with the convex surface on the image side, a second negative, meniscus-shaped lens (2), with the convex surface on the image side, a third positive lens (3), with a convex surface on the object side, a fourth positive, meniscus-shaped lens (4), with a convex surface on the image side, a fifth negative lens (5), with a concave surface on the object side, a sixth biconvex lens (6), a seventh biconcave lens (7), an eighth positive lens (8), with a convex surface on the object side, and a ninth positive lens (9), with a convex surface on the image side.
According to the invention, this task is solved with lenses according to the characteristics of claims 1 to 5. In comparison to the aforementioned systems (see xe2x80x9cBackground of the Inventionxe2x80x9d), a lens according to the invention distinguishes itself in that it maintains all effectivity parameters to adjust to condenser systems and that it affords an improvement in projection quality.
According to claim 1, a lens according to the invention meets the stated requirements, ensuring effective adjustment to condenser systems. The fundamental nature of this part of the invention is described in detail in European patent application 00 100 890.3, which is why it is not further detailed in this document.
The calculation of lenses with shorter focal lengths, while maintaining the same object format and thus larger image angles, has become more and more difficult with respect to the system configuration described in European patent application 00 100 890.3, as astigmatism and image field curvature of the image field""s outer part can no longer be sufficiently corrected. The astigmatic difference and image field curvature have unacceptable values in a range of xc2xe of the image field. The same applies to color aberrations and distortion. Therefore these systems"" excellent corrective condition can no longer be maintained throughout an entire image field. In addition, it is increasingly impossible to meet the requirements necessary for these systems"" installation provisions. This is specifically the case when maintaining a certain minimum value for the last back focal length and a certain minimum overall length, which rises with an increasing image angle. For these reasons, the prevailing basic type of projection had to be further developed after the European patent application and adapted to new conditions.
This development resulted in typical wide angle lenses with an inverse configuration. Such system types have been abundantly described in the aforementioned patents (see xe2x80x9cBackground of the Inventionxe2x80x9d) However, none of them meet the requirements of bundle geometry according to claim 1. The distance between entrance pupil and object plane is preferably always  less than 100 mm, and therefore angle xcex1 RBa is largely negative. In addition, the projection quality of systems in the aforementioned patents (see xe2x80x9cBackground of the Inventionxe2x80x9d) with up to 9 lenses and in part more, is not sufficient for required target values (a contrast of 60 LP/mm greater than 40% throughout an entire image field, distortion xe2x89xa61%). This can mostly be attributed to insufficient correction of astigmatism and image field curvature.
Patents DE-OS 2554963, DE-OS 2306346, DE-PS 2512797, DE-PS 2514081, DE-PS 2436444, DE-OS 2359156, DE-PS 2344224, DE-OS 2254586 as well as patent documents U.S. Pat. Nos. 5,724,195, 5,684,643, 5,625,497 and 5,477,389 describe modified systems of the aforementioned basic types. Essentially they are different in the center part of the lens configuration, as the anterior part preferably begins with two negative menisci and the posterior part concludes preferably with a refractive power sequence (successively from image to object) of one negative lens and two positive lenses. This anterior and posterior configuration can essentially be found in all systems. With respect to the aforementioned previously known systems, a system according to the invention has been successful in maintaining the provisions of bundle geometry according to claim 1 and achieving the necessary increase in projection quality primarily due to the different design of the center system""s configuration (lenses 3 to lenses 6) and due to the special diaphragm position as well as a reduction in vignetting. This way, the system according to the invention was successful in considerably expanding the lens characteristics relevant to European patent application 00 100 890.3 by including shorter focal lengths, and therefore larger image angles, with only 2 additional lenses. Thus, the excellent projection quality of the aforementioned previously known system could be maintained for the same aperture relationship of 1:1.9 throughout the entire new focal length range and could in part be improved further. Excellent projection quality can be achieved independently from image field curvature (slightly curved or flat), as is further illustrated and clarified in an example.
In order to produce a gradual focal length series, which is necessary in order to adjust to projection conditions, using about the same type of glass for equivalent lenses offers a decisive technological advantage. Furthermore, only technologically advantageous, i.e. process and cost effective glass is used.
One preferred application of a projection lens according to the invention is the use of the lens alone, i.e. without additional components. It is entirely usual within the context of the invention to combine separate optical components with the projection lens. These components may, for example, be lens attachments or lens supplements, especially attachments for focal length variation and anamorphic attachments for panorama wide screen projection. It is conceivable to integrate attachments mechanically.